In a similar prior-art metering and spray pump of this class (DE 38,28,811 A1), the valve annular wall that sealingly surrounds the cylindrical generated surface of a projection forming the valve seat of the discharge valve is elastic only radially and can consequently be lifted off only radially. The valve annular walls of the suction valves provided in different designs that can also only be lifted off elastically in the radial direction from the cylindrical generated surfaces forming their valve seat during the suction stroke in order for the medium drawn in to be able to flow into the interior space of the bellows between the corresponding generated surface and the valve annular wall surrounding it.
Such discharge and suction valves have proved to be unsatisfactory in practice for metering and spray pumps of this class especially because an excessive opening pressure is necessary in the case of adequately closing force on the one hand, and on the other hand, because the quality of sealing may be compromised by particles that may become lodged between the valve annular wall and the generated surface surrounded by it. Given the small size of the parts of such pumps--the diameter of a bellows is ca. 12-15 mm and its length is ca. 30 mm--the precision of manufacture is also often insufficient to guarantee the necessary quality of closing of the valves, especially for liquid media. Even small deviations in dimension, in the range of one hundredth of one mm, may lead to rejects.
The other embodiments of suction valves which can be found in the same document, have tongue- or plate-like closing members to cover axial bores, and also fail to meet the requirements imposed on such pumps in terms of reliability of operation.
The sealing or closing quality of the valves is also decisive for performing, especially on automatic assembly machines, a dry function test in which these valves must prove to be air-tight. Moreover containers that are equipped with such metering and spray pumps are subjected, for safety's sake, to drop tests, in which the valves also must prove to close reliably in order to pass the test.
Another decisive property which such metering and spray pumps must possess, is the possibility of manufacturing them economically. Since they are produced in very large lots, it is necessary for them to consist of the smallest possible number of individual parts with economically acceptable manufacturing tolerances, and they should be able to be assembled in the simplest manner possible.
Moreover, the generation of vacuum in the container due to air flowing in during the suction stroke must be avoided in such metering and spray pumps.
In a prior-art metering pump with pump bellows (DE-PS 35,09,178 A1), a ring-like sealing lip is arranged, for the latter purpose, as a radially outwardly directed extension of the lowermost fold of the bellows at the top end of a collar forming the lower end of the bellows. This collar sealingly surrounds an annular collar of the housing part that is or can be connected to the container. In its starting position, the annular sealing lip lies, due to its initial shape, sealingly on the cylindrical inner side of an annular seat, which is made in one piece with the housing part that can be connected to the bottle neck of a container. The function of this sealing lip is that of a one-way valve which allows air to flow into the interior of the container through vent openings during the suction stroke of the pump, on the one hand, but it ensures, on the other hand, that no portion of the liquid or pasty contents of the container will be able to escape to the outside past the outside of the bellows. The vent openings, through which the air drawn in is able to flow into the interior of the container, are arranged in a front wall of the housing part that can be connected to the container. This housing part is usually provided with internal threads which can be screwed onto corresponding external threads of a can- or bottle-like container.
In the case of can- or bottle-like containers, which have high stability of shape that withstands even higher vacuums because of the hardness of their material and/or the wall thickness, there is a risk that the suction function will be compromised if ventilation is insufficient.
However, in the case of containers which are thin-walled and/or consist of a flexible or elastic material, so that they will undergo deformation even under low vacuums, the hitherto known shapes of the annular sealing lips are insufficient for avoiding deformation of the container. This is especially true if the annular sealing lip is to have only a relatively small radial extension in order to obtain a radially compact design. As a result of the elasticity, the opening and closing interplay with the inner surface of the annular wall surrounding it becomes insufficient.
In addition, there is also a risk in the case of thin-walled or readily deformable containers that under the effect of an accidental or unintended radial pressure exerted on the container wall, the annular sealing lip will be subjected inadvertently, as in the case of, e.g., a toothpaste tube, to a much higher pressure in the blocking direction than normally happens when the container with the metering pump attached is brought into the horizontal position or placed upside down. The conventional shapes of the annular sealing lip are no longer able to exert their sealing effect and to withstand the increased pressure in the discharge direction in this case as well. The alternations between air intake under a relatively low vacuum and tight sealing in the opposite direction under increased pressure cannot be achieved solely by shaping or the design of the cross section.